Effects of agroecological practices on soil organic carbon sequestration using synchronic and diachronic approaches in Madagascar

Abstract

Sequestration of soil organic carbon (SOC) in agricultural systems is a key indicator of soil fertility improvement and climate change mitigation at the global scale. In Madagascar, the effect of management conversion from traditional practices to agroecological ones on SOC sequestration remains unclear. The objectives of this study therefore were (i) to assess the effects of agroecological practices, such as agroforestry (AF), tree plantation (TP) and improved farming practices (IFs), on SOC sequestration at the field level; and (ii) to use both synchronic and diachronic approaches to quantify SOC sequestration following the adoption of agroecological practices. For the diachronic approach, two sampling years (2014 and 2018) were used to determine the annual soil carbon sequestration rates with agroecological practices. For the synchronic approach, SOC sequestration arising from agroecological practices was compared to that of reference fields, such as fallow land (FL) and traditional farming practices (TFs). Soil sampling was carried out on 36 fields with agroecological practices and 60 reference TFs and FL fields. The diachronic approach showed that SOC sequestration rates for AF, TP and IFs were respectively, +2.8, +1.6 and -0.9 t C ha^-1 yr^-1. The synchronic approach showed that SOC stock in AF was higher (109.4 t C ha^-1) than in reference TFs (73.8 t C ha^-1) and FL (67.4 t C ha^-1) fields. The SOC stock in IFs (74.8 t C ha^-1) and TP (69 t C ha^-1) was not significantly different compared to reference fields. For Madagascar this study provides a better understanding of soil carbon dynamics at the farm level when agroecological practices are adopted in place of traditional practices.

Keywords

• agroforestry
• compost
• mirs
• sequestration rate
• tree plantation